The hydrolysis of alpha-chlorinated toluene compounds, in particular the hydrolysis of benzyl chloride to benzyl alcohol, is well-known.
In U.S. Pat. No. 4,474,993 a continuous method for the hydrolysis of benzyl chloride to benzyl alcohol is described, whereby the hydrolysis is accelerated in the presence of basic compounds, in particular sodium hydroxide or sodium carbonate. The hydrolysis takes place in countercurrent mode between the aqueous phase containing the hydrolyzing agent and the organic phase containing the benzyl chloride and an inert organic solvent such as toluene. After the hydrolysis, the organic phase is washed with water in a washing zone and the water is extracted with inert solvent in an extraction zone. The resulting product of the hydrolysis is thereafter separated from the organic phase by distillation, by means of two distillation columns connected in series. This method has the disadvantage that an organic solvent is required to extract the hydrolyzed product. Moreover the distillation of the inert solvent is energy consuming. Another disadvantage of the above described alkaline hydrolysis, are the stoichiometric formation of sodium chloride waste liquors that need to be disposed of.
A further problem is the formation of the undesired by-product dibenzyl ether, also known as dibenzyl oxide. The extent of dibenzyl ether formation may vary from about 0.5 to 30% by weight of the final product and is affected by a number of factors such as choice of hydrolyzing agent, temperature, concentration of hydrolyzing agent, and use of inert solvent. Thus, for instance, the use of sodium carbonate as hydrolyzing agent will give rise to a lower relative rate of formation of dibenzyl ether as compared with sodium hydroxide. Furthermore, a higher concentration of hydrolyzing agent generally gives rise to a higher relative rate of formation of dibenzyl ether. The addition of inert solvent, such as toluene, to the benzyl chloride entails a substantial reduction in the formation of dibenzyl ether. Further, a raised hydrolysis temperature will increase the production of dibenzyl ether. Today, environmental and health concerns warrant the use of processes that are more environmentally and toxicologically friendly.
In U.S. Pat. No. 5,728,897 a method is described wherein a mixture of benzyl chloride and water (10-70 mole equivalents) at 80-180° C. is used without adding alkali carbonates or organic solvents with intensive mixing under incomplete conversion. The hydrochloric acid containing aqueous stream can be concentrated with HCl from the photochlorination unit (for toluene chlorination) or converted back into chlorine by hydrochloric acid electrolysis.
Unfortunately the process of U.S. Pat. No. 5,728,897 is characterized by a lower conversion to benzyl and higher byproduct formation compared to the alkaline hydrolysis under otherwise similar conditions (i.e. water to benzyl chloride mole ratio and temperature). As the molar ratio of water to benzyl chloride decreases, the hydrochloric acid concentration and hence its activity increases by a large factor leading to significant amounts of by-products and lower conversion rates. In addition, it is observed that the benzyl alcohol concentration has an optimum during the time course of the conversion. Thereafter the generated benzyl alcohol is mainly involved in byproduct formation.
There remains a need in the art for improved methods for the hydrolysis of alpha-chlorinated toluene compounds, in particular for the manufacturing of benzyl alcohol.
The present invention aims to resolve at least some of the problems mentioned above.
The invention thereto aims to provide an improved process characterized by a high conversion rate, high yield, low by-product formation, which is economically feasible and has an interesting environmental and toxicological profile.